Biological and cultural adaptation to milk digestion

After infancy most mammals stop secreting lactase (the enzyme that breaks down milk’s sugar, lactose) and lose their ability to digest milk. Some humans, however, can digest milk throughout their life because they carry genes that code for lactase persistence (LP). These genes emerged independently, and were selected for, in several populations where milk was a central food staple.

This study examines the genetic, microbiome, and cultural factors that allow adult milk digestion among groups of peoples that are milk-dependent but lack LP genes. Additionally, the study examines whether genes that impact lactose tolerance co-evolved with those that permit the metabolization of high levels of milk-derived sugars. The study provides training opportunities in field, genetic, and computational methods and is relevant to human evolutionary history and public health.

This study collects novel genetic, microbiome, and phenotypic data to expand current knowledge on genetic and cultural adaptations to milk consumption. Cutting-edge functional genomics approaches enable the identification of novel enhancer regions near the lactase gene and near genes involved with sugar metabolism. Genetic data integration allows for the identification of novel genetic variants influencing lactase persistence.

Lactose tolerance tests are applied in tandem with a genome wide association study (GWAS) to identify novel genetic loci linked to milk-induced blood sugar level increases. Gut microbiome sequencing enables the identification of bacteria that aid in digesting lactose and quantifies the extent to which milk preparation practices shape the composition of the gut microbiome.

The study creates a large genomic and phenotypic database that informs the understanding of recent human evolutionary history and gene-culture co-evolution.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.